This is just a bug. Just exit Firefox and go back in or if that doesn't work, clear your %temp% folder by searching up "Run" and deleting all your files in there. Once there and done, restart your computer and run ROBLOX. If that doesn't work, reinstall ROBLOX and if that doesn't work, get a faster Internet if you can afford it.
Who are you people? - https://www.youtube.com/watch?v=CUCi4vcH_Og |